1. Field of the Invention
The present invention relates generally to antenna devices.
2. Description of the Related Art
Magnetic-coupling communication, a representative example of which is NFC (Near Field Communication), is used in mobile information terminals, such as smartphones and wearable terminals. To implement such communication feature, an antenna is mounted on such a mobile information terminal. With increasing miniaturization and functionality of such mobile information terminals, demand for more compact, slimmer antennas mounted thereon is also increasing.
With regard to antennas, a magnetic antenna formed by looping a flexible substrate, on which a coil conductor is formed, around and along the surface of a magnetic core, is disclosed in Japanese Unexamined Patent Application Publication No. 2010-056982 (Patent Document 1), for example. In this magnetic antenna, the magnetic core has a plate-like shape having at least two parallel sides; the coil conductor, whose conductor opening is the center of the loop, has a rectangular spiral shape having at least two parallel sides. In this magnetic antenna, the flexible substrate is bent along two sides, which are apart from the center of the conductor opening, of the coil conductor and along the two sides of the magnetic core. However, such an antenna is disadvantageous in that when a metal is present near the antenna, magnetic flux is impeded by a demagnetizing field induced by an eddy current, causing degradation in performance of magnetic coupling communication.
Under the circumstances, for example, Japanese Unexamined Patent Application Publication No. 2006-050522 (Patent Document 2) discloses the following magnetic sensor antenna for receiving a magnetic field component of an electromagnetic wave. The antenna, which is to be placed inside a casing and includes a magnetic core formed of a magnetic member and a conductive wire wound around the magnetic core, is configured such that each end, at which magnetic flux density is high, of the magnetic core is bent in a direction away from an adjacent portion of the casing or an adjacent metal component inside the casing. Such an antenna is less susceptible to a metal because the conductive wire is wound around the magnetic member.
However, although the structure of the above-descried conventional magnetic antenna, in which the conductive wire is wound around the magnetic core formed of the magnetic member, makes the magnetic antenna less susceptible to an influence of a metal present near the antenna, the structure disadvantageously narrows communication coverage area in a direction perpendicular to the direction, in which the conductive wire is wound.
Therefore, there is a need for an antenna device less susceptible to a metal present near the device or the apparatus and providing a wider communication coverage area.